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Materials Science in Additive Manufacturing TPMS for perfect sound absorption

Figure 18. The NRC of TPMS structures
Abbreviations: NRC: Noise reduction coefficient; TPMS: Triply periodic minimal surface

Table 10. Sound absorption characteristics of graded triply between uniform primitive and GP structures indicates
periodic minimal surface (TPMS) structures that the graded design method can enhance the average
sound absorption coefficient of the primitive structure. The
Specimen Thickness, Frequency Absorption λ peak /T
T (mm) at first at first peak, enhanced mechanism of graded porous structures with
peak, α 1 larger pore sizes on the incident wave side is attributed to
f 1 (Hz) the impedance-matching effect. Large pores near the sound
GP-12 mm-Ⅰ 12 4980 0.557 5.81 source facilitate the propagation of acoustic waves into the
GP-18 mm-Ⅰ 18 3200 0.670 6.03 graded porous structures, resulting in reduced reflection
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GP-24 mm-Ⅰ 24 2080 0.846 6.96 and increased acoustic energy. In contrast, the enhanced
mechanism of graded porous structure with smaller pore
GP-30 mm-Ⅰ 30 1660 0.847 6.98 sizes on the incident wave side is attributed to Helmholtz-
GP-12 mm-Ⅱ 12 5970 0.452 4.85 like resonance, resembling a Helmholtz resonator
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GP-18 mm-Ⅱ 18 4450 0.581 4.34 composed of a neck (an aperture in a large surface with
GP-24 mm-Ⅱ 24 4000 0.758 3.62 low porosity) and a cavity with high porosity.
GP-30 mm-Ⅱ 30 3520 0.682 3.29 The ranking of the NRC of TPMS structures
Multicavity-GP-Ⅰ 30 1970 0.873 5.88 with multicavity is as follows: multicavity-
Multicavity-GP-Ⅱ 30 1200 0.618 9.65 IWP > multicavity-GP-Ⅱ > multicavity-gyroid
Abbreviation: GP: Graded primitive. > multicavity-GP-Ⅰ > multicavity-diamond > multicavity-
primitive. Multicavity-IWP has the highest NRC
500 – 6300 Hz for diamond structures is the best among the (NRC = 0.732) among all the TPMS structures in this study.
four kinds of uniform TPMS structures, while primitive Despite the enhanced average sound absorption coefficient
structures have the lowest average sound absorption of multicavity-primitive structures, their NRC remains
coefficient among the uniform TPMS structures. For the the lowest among the multicavity-TPMS structures
GP design, the NRC of GP-12 mm-Ⅰ, GP-18 mm-Ⅰ, and mentioned above. To improve the sound absorption of
GP-24 mm-Ⅰ are 0.189, 0.293, and 0.416, respectively; these primitive structures, the multicavity design was applied to
values are similar to the NRC of diamond structures with the primitive structure, leading to NRC of 0.572 and 0.698
the same thickness. Diamond structures with 85% porosity for multicavity-GP-Ⅰ and multicavity-GP-Ⅱ, respectively.
manufactured by stereolithography also demonstrated Compared with Primitive-30 mm, the multicavity design
the best sound absorption among diamond, gyroid, of types Ⅰ and Ⅱ enhanced the noise reduction coefficient
and primitive structures[16]. The comparison of results by 72.3% and 110.2%, respectively. Compared with

Volume 4 Issue 1 (2025) 17 doi: 10.36922/msam.5737